Conformable bandage

ABSTRACT

A warp knitted fabric is described in which each individual wale contains stitches formed from both elastic and inelastic yarn. The fabric is extensible in the direction of the wales and may be used as a substrate in an orthopaedic splinting bandage. Orthopaedic splinting bandages are also described which comprise the warp knitted fabric coated with a hardenable resin such as an isocyanate terminated propolymer. The lengthwise extensibility of the substrate makes the uncured bandage conformable during application to the body.

The present invention relates to a knitted fabric which is suitable foruse as a substrate in hardenable orthopaedic splinting bandages. Thepresent invention also relates to an orthopaedic bandage comprising aresin-coated fabric substrate which has improved conformability.

Conventional orthopaedic splinting bandages for use in the treatment ofbone fractures or other conditions requiring immobilization of part ofthe body are formed from a substrate impregnated with a substance whichhardens to a rigid structure after wrapping the bandage around the body.Traditionally Plaster of Paris has been used but more recently certainplastics have gained acceptance as replacements for Plaster of Paris.Such new bandages are lighter, waterproof and permeable to X-rays.Substrates for use with these plastics have included glass fibre fabricssuch as those described in U.S. Pat. Nos. 4,502,479, 4,609,578,4,668,563 and 4,323,061.

One disadvantage of substrates including glass fibres is that the castsformed from them can become brittle and break down during wear and henceneed to be replaced before healing is complete. A second disadvantage isthat during cast removal irritating glass dust or fibres may begenerated. These disadvantages would be mitigated by using a substratewhich gave a durable cast and did not give rise to irritating fibres oncast removal. However, heretofore such substrates have lacked theconformability and cast strength found when using glass fibresubstrates.

A knitted fabric has now been made containing individual wales knittedfrom elastic yarn and inelastic yarn and when using this fabric as asubstrate a bandage is achieved which has good conformability comparedto those employing existing fabric substrates. Even more surprisinglythe cast formed using this novel substrate does not slow a loss ofstrength compared to a cast which employs a glass fibre substrate. Afurther advantage of this fabric is that it is found to possesssurprisingly good dimensional stability that is it has little or nopropensity to curl which aids processing such as coating.

Although the presence of wales which are knitted from both elastic andinelastic yarns is most useful in substrates which do not contain glassfibres it is envisaged that the same construction could be used withglass fibres to advantage.

The present invention provides a warp knitted fabric which containswales which are knitted from both elastic and inelastic yarns.

The warp knitted fabric of the invention is an elastic fabric that is tosay that it possesses recoverably extensibility in a direction parallelto the wales which contain the elastic yarn. An elastic yarn is a yarnformed form an elastomer. An elastomer may be defined as a rubber orpolymer which has high extensibility together with rapid andsubstantially complete elastic recovery. Suitable elastic yarns for usein the invention include those which have an elongation at break ofgreater than 100% and more suitably, greater than 300%.

The warp knitted fabric of the invention is described herein withreference to its use as a substrate in an orthopaedic bandage. It isenvisaged that the fabric may be used in other applications where itselastic properties may be employed to advantage, for example in bandagesand clothing.

In one favoured aspect therefore the present invention provides a warpknitted fabric suitable for use as a substrate in a resin coated, waterhardenable orthopaedic splinting bandage which fabric contains waleswhich are knitted from both elastic and inelastic yarns.

In a second aspect the present invention provides a conformablehardenable orthopaedic sprinting bandage comprising a warp knittedfabric substrate coated with a curable resin which fabric substratecontains wales knitted from both elastic and inelastic yarns. Mostsuitably the resin is a water curable resin so that the bandage is onewhich hardens after being exposed to water.

It is clear from the above that each individual wale is knitted fromboth elastic and inelastic yarns. The fabric normally has a planarsurface.

The orthopaedic splinting bandages of the present invention possesslengthwise extensibility by virtue of the presence of elastic yarnsknitted into the wales of the fabric. Suitable elastic yarns includethose formed from natural rubber or a synthetic elastomer such aspolyisoprene, polybutadiene, copolymers thereof, elastomericethylene-propylene copolymers and thermoplastic elastomers includingblock copolymers of styrene and butadiene or isoprene or an elasticpolyurethane yarn. A particularly preferred elastic yarn is a spandexyarn, that is a polyurethane yarn for example Lycra yarn (Trade mark).

The inelastic yarns of the knitted substrate may be formed from yarnswhich include yarns formed from polypropylene, polyester, polyamide,polyethylene, cotton viscose. A preferred yarn is polyester yarn,including multifilament or monofilament polyethylene terephthalate yarn.

A wale when used herein- means a column of loops along the length of thefabric. In the fabric of the invention some of the loops in each waleare formed from either elastic yarn and some formed from inelastic yarnand are preferably knitted in a repeating pattern along the wale. Whennot being knitted as a loop the yarn mislaps until required for knittingagain. The non-knitted yarn may be laid into the knitted stitches or maybe allowed to float on the surface of the fabric. Typically in a 4 barwarp knitted fabric there may be 2 polyester stitches to 1 elastomerstitch or vice versa. This is unlike previously known elastic fabricswhere either all the loops of the wales are formed from elastic yarn orelastic yarn is incorporated as an inlay along a wale formed frominelastic yarn. This new manner of knitting surprisingly gives theadditional advantage of dimensional stability, shown by lack of inwardcurl, over a wider range of mesh dimensions.

Suitably the lengthwise extension of the substrate that is in thedirection of the wales, may be from 15 to 200%, more suitably 25 to 160%and preferably 50 to 150%. The degree of extension may be variedaccording to the type of elastic yarn chosen but the above ranges aresuitable for substrates used in orthopaedic bandages.

When coated with resin the lengthwise extension can be at least 25%,more suitably at least 40% and preferably at least 50%. The upper limitto lengthwise extensibility can be 60%, more suitably 70% and preferablyat least 80%.

Suitably the widthwise extension of the substrate may be from 20 to150%, more suitably 20 to 100%, most suitably 25 to 60% and preferably30 to 50% for example 45%.

The elastic yarns in the substrate appear to cause the substrate toreturn to its original length after stretching and so facilitateconformability of the substrate to the patient's body. The bandages wereobserved to conform easily to various shaped formers made to representparts of the body.

Suitably the knitted substrate has a low power, that is the forcerequired to stretch the substrate for a given percentage extension. Ifthis power is low then this will help to prevent constriction of thepatient's limb after the bandage has been applied.

The lengthwise extension may be measured using an Instron TensileTesting Machine. A 10 cm length of substrate may be clamped in the jawsof the machine and the jaws separated at constant speed. A conventionalstress-strain curve for the substrate may be recorded. The extension ata given load and the load required to give a given extension can becalculated from the curve for the substrate under test.

For the best shelf life of the resin coated substrates, the elastic yarnused in the substrate must be compatible with the resin with which it iscoated. Suitable compatible elastic yarns may be identified by forming abandage incorporating the elastic yarns and coating with the resin andageing in a sealed container for 12 weeks at 55° C. If at the end ofthis time the bandage may be used to form a satisfactory cast then theelastic yarn is suitable particularly for use in conjunction with theresin. The unsuitability of some elastic yarns may be overcome by meansof coating or wrapping the yarn with other inert materials such ascotton or nylon yarn. For example elastic polyurethane yarns may bewrapped in cotton or nylon.

Suitably the substrate may have a thickness of from 0.375 mm to 4.0 mm,more suitably will be 0.50 mm to 3.00 mm thick and preferably 1.00 mm to2.00 mm thick, for example 1.50 mm.

Suitably the knitted substrate may have a weight per unit area whenrelaxed of from 50 to 500 gm⁻² more suitably may have a weight of from100 to 350 gm⁻², and preferably a weight of between 150 and 220 gm⁻² forexample 170 g, 175, 180, 185 and 190 gm⁻².

Suitably the fabric may be produced on a warp knitting machine or on acrochet knitting machine. The fabric is a warp knitted fabric comprisingchain or pillar stitches linked by under-lapped inlay threads. In thefabric of the invention the elastic yarn is incorporated in the pillarstitch so as to give the lengthwise stretch.

Normally when producing a pillar or chain stitch in a warp knittedfabric the same yarn guide always overlaps the same needle. Thisproduces chains of loops in unconnected wales which are then connectedtogether by underlaps of yarn from second or other guide bars to formthe fabric. When the elastic yarn is present at least two yarn guidesare used to produce each pillar stitch. The first guide feeds thein-elastic yarn to the needle which knits one or more courses beforebeing withdrawn to let in the second guide which feeds in the elasticyarn to the needle which again knits for one or more courses before thesecond guide withdraws and the first guide is let in. This cycle isrepeated as knitting proceeds. The knitting provides a stable fabricwith a reduced tendency to curl.

The resins used in the orthopaedic bandage of the invention may be anycurable resin which will satisfy the functional requirements of anorthopaedic cast. The preferred resins are those cured with water ormoisture and include the resins described in U.S. Pat. Nos. 4,667,661,4,502,479, 4,574,793, 4,433,680, 4,427,002, 4,411,262, 3,932,526,3,908,644, 3,630,194, in German Offenlengungsschrift No. 2651089 and inEuropean Patent Applications Nos. 35517, 57988, 86621 and 94222.

Aptly the resin used to coat the fabric substrate may be a water curableisocyanate terminated prepolymer system. Among suitable prepolymersystems are those identified in U.S. Pat. Nos. 4,411,262, 4,427,002,4,433,680 and 4,574,793. Particularly preferred are those systemsdisclosed and claimed in U.S. Pat. Nos. 4,427,002 and 4,574,793 thedisclosures of which are incorporated herein by cross-reference.

Suitably the bandage may be formed by coating or impregnating thesubstrate with the resin in the manner described in those patents,particularly in U.S. Pat. No. 4,427,002.

Suitably the weight of resin on the substrate is from 150 to 650 gm⁻²and mare suitably from 150 to 500 gm⁻², most suitably a weight of 200 to450 gm⁻² and preferably 225 to 450 gm⁻² most preferably between 250 to400 gm⁻². The weight of resin may be chosen so that suitably 40 to 60%of the total weight of the bandage is resin and more suitably 55 to 60%of the total weight. Thus if the fabric weight is 180 gsm and the resincoating is 55-60% of the bandage then the weight of resin taken is220-270 g.

The formed bandages may be packaged by heat sealing in waterproofpouches such as those formed from metal foil polyethylene laminates orpolyethylene pouches.

In use the bandages may be brought into contact with water and wrappedaround the injured part of the body. The setting bandage has a workingtime which is sufficient to allow the bandage to be positioned on thelimb and a set time which is the tine taken for the cast to becomerigid. Apt working times are 1 to 6 minutes and apt set times are 5 to30 minutes.

The cast incorporating the substrate of the invention is readilyremovable by conventional means such as by cutting with a conventionalcircular saw. Large casts may be removed using a single cut along thelength of the cast which is not always achievable with fibre glasssubstrate casts.

The build-up of strength in the cast was assessed by wrapping theresin-coated substrate round a former to make a cylinder. The former isremoved and the cylinder wall clamped in a Instron Tensile Testingmachine so as to measure diametral compression and extension forces. Themachine is adapted so that the moving clamp would oscillate betweenpositions 2.5 mm from the rest position. The force required to deformthe cast as it set over a period of time is measured. The results wererecorded an a chart recorder. A bandage formed according to Example 2,which was 4 layers thick, was tested in comparison with a conventionalglass fibre based bandage using cylinders formed of 5 layers of bandage.The bandage according to the invention was greater in strength to theglass fibre bandage both on initial setting and after 24 hours.

    ______________________________________                Rigidiy (kg/cm width)                Time after initiation of set                 15 mins  30 mins 24 hr    ______________________________________    Bandage of Example 2                   2.7        3.4     5.3    (4 layers)    Glass fibre-based                   2.1        2.65    4.5    bandage (5 layers    ______________________________________

For the following examples the knitting machine has 12 needles per inchand is threaded half sett. The knitting notation is an English notation.

EXAMPLE 1 Preparation of substrate

A substrate was prepared by knitting together elastic polyurethane yarnsand polyester yarns. The elastic polyurethane yarns were formed from asegmented polyurethane and are available as Lycra spandex yarns. Theyarns had a weight per unit length of 156 dtex. The yarns may be wrappedin nylon or cotton or other yarns. The polyester was a multifilamentpolyethylene terephthalate with a weight per unit length of 1100 dtex.

The knitting pattern was as follows:

    ______________________________________    Bar 1    1-0/0-1/1-1      (Polyester yarn)    Bar 2    0-0/1-1/1-0      (Lycra yarn)    Bar 3    3-3/2-2/3-3/0-0/1-1/0-0                              (Polyester yarn)    Bar 4    0-0/1-1/0-0/3-3/2-2/3-3                              (Polyester yarn)    ______________________________________

The machine was 12 gauge and each guide bar was threaded half sett.

The fabric so knitted has 30 to 34 wales/10 cm width and 35 to 43courses/10 cm. The fabric was knitted at a 10 cm width. The fabric has aweight per unit area of 200 gm⁻².

The knitted fabric has an extension in the width direction of 80% andextension in the lengthewise direction of 50% (approx.).

This fabric is suitable for use as a substrate in an orthopaedicsplinting bandage.

EXAMPLE 2 Preparation of Bandages

A water curable polyurethane resin system comprising a polyurethaneprepolymer described in U.S. Pat. No. 4,574,793 as prepolymer A andcontaining methane sulphonic acid as stabiliser and bis (2,6 dimethylmorphilino) diethyl ether as catalyst is coated onto a knitted fabricdescribed in Example 1 using the process described in U.S. Pat. No.4,427,002. The weight of the resin applied is 240 gm⁻² which means thatthe resin forms 55% of the weight of the bandage. The coated bandage hada lengthwise extension of 25% approximately.

The bandage strip is cut into 3 meter lengths and spooled onto rolls.The bandage rolls are then placed into pouches which are heat sealed toprevent exposure of the contents to moisture.

A bandage is made into a cast by dipping the bandage roll in water andwrapping around a body member.

EXAMPLE 3 Preparation of Substrate

A fabric was prepared by knitting together elastic polyurethane yarnsand polyester yarns. The elastic polyurethane yarns are formed from asegmented polyurethane and are available a-s Lycra spandex yarns and maybe wrapped in nylon or cotton. The yarns had a weight per unit length of156 dtex. The polyester was a multifilament polyethylene terephthalatewith a weight per unit length of 1100 dtex.

The knitting pattern was as follows:

    ______________________________________    Bar 1    1-1/1-1/1-0/0-0/0-0/0-1                               (Lycra fibre)    Bar 2    1-0/0-1/1-1/1-0/0-1/1-1                               (Polyester fibre)    Bar 3    3-3/2-2/3-3/0-0/1-1/0-0                               (Polyester fibre)    Bar 4    0-0/1-1/0-0/3-3/2-2/3-3                               (Polyester fibre)    ______________________________________

The machine was 12 gauge and each guide bar was threaded half sett.

The fabric knitted according to this pattern has a weight per unit areaof 175 gm⁻², 30 to 34 wales/10 cm width and 35 to 43 courses/10 cmlength.

This fabric is suitable for use in an orthopaedic splinting bandage.

EXAMPLE 4 Preparation of Bandages

A bandage was prepared using the fabric described in Example 3 as thesubstrate in the manner described in Example 2.

EXAMPLE 5 Preparation of Fabric

A fabric was prepared by knitting together an elastic polyurethane yarnand polyester yarns. The elastic polyurethane yarn was formed from asegmented polyurethane available as a Lycra spandex yarn. The yarn had aweight per unit length of 156 dtex. The fibres may be wrapped in nylonor cotton or other suitable yarns. The polyester was a multifilamentpolyethylene terephthalate with a weight per unit length of 1100 dtex.

The knitting pattern was as follows:

    ______________________________________    Bar 1      Polyester   1-0/0-1/1-1    Bar 2      Lycra       0-0/1-1/1-0    Bar 3      Polyester   3-3/2-2/3-3/0-0/1-1/0-0    Bar 4      Polyester   0-0/1-1/0-0/3-/2-2/3-3    ______________________________________

The machine was 12 gauge and each guide bar was threaded half sett.

The knitting machine was set to knit 4.0 courses/cm. In the wales, theknitting was such that the Lycra stitch was the first stitch after theinlay crossover. The repeat pattern in the pillar stitch was 2polyester:1 Lycra stitch.

The knitted fabric has an extension in the width direction of 75-80% andthe extension in the lengthwise direction is 50% (approx).

The fabric is suitable for use as a substrate in an orthopaedicsplinting bandage.

EXAMPLE 6 Preparation of Fabric

A fabric was prepared in a similar manner to and from the same yarns asdescribed in Example 5 except that Bar 1 carried the elastic yarn andBar 2 carried a polyester yarn. In this construction the pillar stitchrepeat is now 2 Lycra stitches:1 polyester stitch. The polyester stitchis positioned on the inlay cross-over. When not knitting the guide bar 2in-lap the polyester yarn inside the Lycra stitches.

The fabric has similar characteristics to that prepared as in Example 5.

EXAMPLE 7 Preparation of Fabric

A fabric was prepared from similar materials as those described inExample 5.

The knitting pattern was as follows:

    ______________________________________    Bar 1      Polyester  0-0/1-1/1-0    Bar 2      Lycra      1-0/0-1/1-1    Bar 3      Polyester  3-3/2-2/3-3/0-0/1-1/0-0    Bar 4      Polyester  0-0/1-1/0-0/3-3/2-2/3-3    ______________________________________

The machine was 12 gauge and each guide bar was threaded half sett.

In this construction the pillar stitch repeat is two Lycra stitches:1polyester stitch. The polyester stitch is positioned on the inlaycross-over point. When not knitting the guide bar 2 allows the polyesteryarn to float on the surface of the fabric rather than to inlay up thepillar stitch inside the Lycra stitches.

The fabric has similar characteristics to that prepared in Example 5.

EXAMPLE 8 TO 11 Preparation of Fabric

Suitable fabrics are prepared by using polypropylene yarn with the sameknitting patterns described in Examples 1, 5, 6 and 7. The polypropyleneyarn used is a 70 filament yarn of weight per unit length of 470 dtex.

EXAMPLE 12 Preparation of Bandages

A resin was formed from Isonate 143L (47.8%), Isonate 240 (14.7%),Voranol (3.5%), propylene glycol (31.9%), antifoam (0.3%), methanesulphonic acid (0.03%) and bis (2.6-dimethyl morpholino-N-ethyl) ether(1.8%).

The resin was spread at 54% by weight of the weight of the total bandageonto the substrate described in Example 1 (10 cm×10 cm) using a hopperand doctor knives in a conventional manner under nitrogen. The bandagewas wound onto a core to form a roll and sealed into an aluminium foilpouch under argon.

A bandage was removed from a pouch and immersed in water. The bandagewas squeezed three times under water to ensure wetting, removed, shakenand applied to a mandrel. The bandage provided a suitable cast.

EXAMPLE 13 TO 20 Preparation of Bandages

A resin as described in Example 12 was applied to fabrics described inExamples 3, 5 to 11 by the process described in Example 12. The coatedsubstrates provided suitable bandages for forming casts.

I claim:
 1. A conformable, hardenable, orthopaedic splinting bandagecomprising a warp knitted fabric substrate coated with a curable resinwherein said fabric substrate contains individual wales, each individualwale comprising a repeating pattern of loops knitted from an elasticyarn and an inelastic yarn, said elastic yarn or inelastic yarnmislapping when not knitted to form said loops.
 2. A bandage as claimedin claim 1 wherein said curable resin is a water curable resin.
 3. Abandage as claimed in claim 2 wherein said water curable resin is anisocyanate terminated prepolymer.
 4. A bandage as claimed in claim 1wherein in each wale of the fabric substrate, the elastic or inelasticyarn which is not being knitted as a loop is laid into the knittedstitches of a yarn which is being knitted as a loop.
 5. A bandage asclaimed in claim 1 wherein in each wale of the fabric substrate, theyarn which is not being knitted as a loop is allowed to float on thesurface of the fabric.
 6. A bandage as claimed in claim 1 wherein therepeating pattern along the wale is 2 inelastic yarn loops to 1 elasticyarn loop or 2 elastic yarn loops to 1 inelastic yarn loop.
 7. A bandageas claimed in claim 1 wherein the coated bandage has an extension of atleast 25%.
 8. A bandage as claimed in claim 1 wherein the substrate hasa weight per unit area of 100 to 350 gm⁻² and the resin is 40 to 60% ofthe total weight of the bandage.